Bulletin of the American Physical Society
2005 TSAPS/AAPT/SPS Joint Fall Meeting
Thursday–Saturday, October 20–22, 2005; Houston, TX
Session B3: General Experimental II |
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Room: Waldorf Astoria B 210B |
Friday, October 21, 2005 2:00PM - 2:12PM |
B3.00001: Thermodynamics and Anharmonicity in Dilute Vanadium Alloys Jorge Munoz, Olivier Delaire, Brent Fultz The specific heats of elemental vanadium and dilute vanadium alloys with the same body-centered cubic crystal structure were measured by differential scanning calorimetry (DSC) from room- temperature to 1673K. The results were compared to the harmonic phonon contribution to the total heat capacity, which was obtained from the phonon densities of states (DOS), previously measured using inelastic neutron scattering. The anharmonic entropy of V93-Co7 was calculated from the DSC measurements and compared to the one obtained from the phonon DOS and Thermo- Mechanical Analyzer (TMA) measurements. [Preview Abstract] |
Friday, October 21, 2005 2:12PM - 2:24PM |
B3.00002: Electromagnetically Induced Transparency in Cesium Molecule Hui Chen, Vladimir Sautenkov, Yuri Rostovtsev, Hebin Li, Marlan Scully Experimental results about electromagneitcally induced transparency in cesium molecule is reported here. Subnatural peak is obtained by optical pumping. The relation between peak width and density of cesium molecule is studied. [Preview Abstract] |
Friday, October 21, 2005 2:24PM - 2:36PM |
B3.00003: Gallium NMR Study of Type-I Clathrates Weiping Gou, Yang Li, Ji Chi, Joseph H. Ross, G.S. Nolas Clathrates are open framework structures containing guest atoms inside cages composed of silicon, germanium, or tin forming a crystalline framework. We carried out Ga NMR measurements on type-I clathrates, including Sr$_{8}$Ga$_{16}$Ge$_{30}$, Ba$_{8}$Ga$_{16}$Ge$_{30}$, Ba$_{8}$Ga$_{16}$Sn$_{30}$ and Ba$_{8}$Ni$_{4}$Ga$_{12}$Ge$_{30}$. For a Ba$_{8}$Ga$_{16}$Ge$_{30}$ sample with low carrier density, we find that the relaxation behavior ($\textit{T$_{1}$}$) deviates from the Korringa relation, and the Knight shift and linewidth change with temperature. These results could be explained by carrier freezout in the Ba clathrate, and the development of a dilute set of magnetic moments due to these localized carriers. In the Sr clathrate, on the other hand, we see ordinary metallic behavior. In addition we see effects of slow atomic motion attributed to the dynamics of guest atoms in the cages. In Ba$_{8}$Ga$_{16}$Sn$_{30}$ and Ba$_{8}$Ni$_{4}$Ga$_{12}$Ge$_{30} $ samples, we observed 2 NMR peaks which correspond to 2 sites on the framework of clathrates, in contrast to the Sr$_{8}$Ga$_{16}$Ge$_{30}$ and Ba$_{8}$Ga$_{16}$Ge$_{30}$ clathrates for which a single site is observed. This work was supported by the Robert A. Welch Foundation, Grant No. A-1526, and by the NSF (DMR-0103455). [Preview Abstract] |
Friday, October 21, 2005 2:36PM - 2:48PM |
B3.00004: How the Cookie Crumbles: Data Analysis for Experimental Granular Materials Research Victoria Winbow, R.J. Zieve Granular materials are characterized as a conglomeration of macroscopic particles which experience a loss of energy upon interaction, while being large enough to avoid thermal motion fluctuations. Despite centuries of study, their behavior is still mysterious. Theoretical work has traditionally focused on spheres and hard ellipsoids rather than simple polygons or polyhedra. Previous experimental research on polygons created from lattices of welded ball bearings had indicated a link between angle and density in two dimensions immediately prior to an avalanche. The goal of this project was to confirm those findings and attempt to determine what portion of the material was responsible for the correlation. Code was written to analyze photos of a rotating frame containing a sample granular material, making it possible to find density and angle for regions of arbitrary size and calculate correlations from them. Correlations for various granular shapes were most visible when taken over large regions and decreased in smaller regions as noise became dominant with one notable exception. [Preview Abstract] |
Friday, October 21, 2005 2:48PM - 3:00PM |
B3.00005: Magnetic and Physical Properties of Nd$_{2}$Ni$_{2}$Pb and NdNiPb V. Goruganti, Yang Li, Joseph H. Ross, Jr., K. D. D. Rathnayaka, Y. Oner We report magnetic, transport and thermodynamic measurements for Nd$_{2}$Ni$_{2}$Pb and NdNiPb, which are members of recently-discovered $R$-Ni-Pb families of intermetallics. In Nd$_{2}$Ni$_{2}$Pb a $\lambda$ type specific heat jump was observed at 19 K corresponding to an antiferromagnetic transition. Magnetization measurements show this phase to have a canted structure, with a metamagnetic transition to an aligned phase in $H$ = 3 T at low temperatures. We have further explored the metamagnetic transition using field dependent specific heat. The single antiferromagnetic phase stands in contrast to the more complex magnetic structures observed in the heavy-rare-earth members of this family. At high temperatures the magnetization obeys a Curie law and the estimated magnetic moment agrees with the free ion moment of Nd. Resistivity measurements were conducted in the presence of an applied magnetic field and a kink was observed at 19 K. We performed similar measurements on NdNiPb and observed an antiferromagnetic transition at 5 K. A high temperature Curie fit showed that Ni is non-magnetic, while resistivity measurements show a kink at the transition temperature. This work was supported by the Robert A. Welch Foundation (grant A-1526), the National Science Foundation (DMR-0103455), and by the Texas A\&M University Telecommunications and Informatics Task Force. [Preview Abstract] |
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